Masahiro Mita

Evolution of Atomically Stepped Surface of Indium Tin Oxide Thin Films Grown on Nanoimprinted Glass Substrates

Indium tin oxide (ITO) thin films were deposited on atomically stepped glass substrates (step height of ~0.2 nm and separation of ~80 nm) by pulsed laser deposition. The atomically stepped glass was prepared via thermal nanoimprint using an atomically stepped sapphire mold. The surface morphology of the ITO thin film definitely reflected the atomically stepped pattern of the glass substrate surface. The step height and the separation of the ITO film surface were close to those of the nanoimprinted glass surface. The fast Fourier transform analysis of the atomic force microscopy image also confirmed the periodicity of the atomic-step pattern.

Formation of 0.3-nm-high stepped polymer surface by thermal nanoimprinting

We performed atomic-scale surface patterning with a vertical resolution of approximately 0.3 nm on a poly(methyl methacrylate) (PMMA) polymer sheet (10 × 10 mm2) by thermal nanoimprinting using an atomically stepped sapphire template (α-Al2O3 single crystal). The sapphire mold with () r-plane exhibited regularly arranged straight steps with a uniform height of approximately 0.31 nm. The template nanopattern could be transferred onto the surface of the PMMA sheet under the imprinting conditions of 0.2 MPa load for 300 s at 140 °C. Atomic stairs with approximately 0.26-nm-high straight steps and approximately 600-nm-wide terraces were formed on the PMMA surface.

Nanoimprint Fabrication and Thermal Behavior of Atomically Ultrasmooth Glass Substrates with 0.2-nm-Height Steps

We examined the conditions for the development of atomically stepped ultrasmooth surfaces on commercial silicate glass substrates by the thermal nanoimprint technique using sapphire (α-Al2O3 single crystal) molds with 0.2-nm-height atomic steps. Under the pressing conditions of 3 MPa, 300 s, and 610 °C for imprinting, a 0.2-nm-high stepped and atomically ultrasmooth terraced surface could be formed on soda-lime silicate glass substrates having the glass transition temperature of 521 °C. We found that the 0.2-nm-height step structure of the imprinted glass surface disappeared after annealing at 490 °C, and the smoothness of the terrace increased.

Fabrication of nanostructured ITO thin films on nanoimprinted glasses by pulsed laser deposition

We fabricated indium tin oxide (ITO) thin films on nanoimprinted glass substrates using pulsed laser deposition (PLD). The nanoimprinted glass substrate was prepared by thermal nanoimprint using an atomically stepped sapphire (α-Al2O3 single crystal) mold. Two kinds of sapphire molds were employed, one with a single step about 0.2 nm high and the other with a bunched step about 2 nm high. The surface morphology of the stepped sapphire mold was successfully transferred to the glass surface in an atomic scale. The nanoimprinted glass had a regular nanostepped pattern; one had a step height of about 0.2 nm and step separation of about 100 nm, the other had a step height of about 2 nm and step separation of about 1 μm. The ITO films were deposited at room-temperature (RT) or 200°C on the nanoimprinted glass substrates and on the non-patterned commercial glass for comparison. The ITO films deposited at RT were post-annealed for further crystallization. The surface of the ITO thin films deposited on the nanoimprinted glass well reflected the nanopattern of the glass substrate surface. Preferential crystalline orientation of the ITO thin films was achieved on the nanoimprinted glass substrates. The resistivity of ITO thin films deposited on the nanoimprinted glass was lower than that on the commercial glass, which was probably due to the higher crystal orientation of the films grown on the nanoimprinted glass surfaces.